1. Field of the Invention
This invention relates generally to a vehicle powertrain, and, in particular, to controlling a ratio change with active damping of an off-going clutch of a dual input clutch transmission.
2. Description of the Prior Art
A dual clutch transmission (DCT), also called a powershift transmission, is a geared mechanism employing two input clutches used to produce multiple gear ratios in forward drive and reverse drive. It transmits power continuously using synchronized clutch-to-clutch shifts.
The transmission incorporates gearing arranged in a dual layshaft configuration between the transmission input and its output. One input clutch transmits torque between the input and a first layshaft associated with even-numbered gears; the other input clutch transmits torque between the transmission input and a second layshaft associated with odd-numbered gears. The transmission produces gear ratio changes by alternately engaging a first input clutch and running in a current gear, disengaging the second input clutch, preparing a power path in the transmission for operation in the target gear, disengaging the first clutch, engaging the second clutch and preparing another power path in the transmission for operation in the next gear.
Controlling noise vibration and harshness (NVH) in a vehicle powertrain that includes a powershift transmission is a challenge due to the lack of a damping device such as a torque converter located in a drive path between the engine and transmission. Seamless control of gear shifts while a powershift vehicle is operating is essential toward realizing the expected performance, fuel economy and NVH comfort. Due to the physical structure of the powershift transmission, especially in a dry clutch application, gear rattle associated with gear shift is a potential problem, especially when engaging a pre-selected gear during a gear shift.
A need exists in the industry for a gear shift control that minimizes gear rattle noise during a gear shift of a powershift transmission, preferably by providing active damping of an input clutch during the gear shift.